In recent years, a variety of sensors for sensing the touch of a person's body part or for reading a person's biometric information have been developed. A capacitive sensor has been developed as one such sensor. When a person's body part is placed in contact with or in close proximity to the sensor surface, the capacitive sensor detects a change in capacitance and thereby detects the touch of the body part or converts height variations on the surface of the body part into electrical signals. Such capacitive sensors are widely used, for example, as touch sensors, touch pads, touch panels, fingerprint sensors, etc. (refer, for example, to U.S. Pat. No. 5,325,442, Japanese Laid-open Publication No. 2001-222706, Published Japanese Translation of PCT application No. 2001-525067, Japanese Laid-open Publication No. 2001-56204 and Published Japanese Translation of PCT application No. 2005-505065).
A touch sensor is a sensing device that detects the touch of a person's body part such as a finger when it touches the sensor surface. A touch pad is a device that detects the position at which the sensor surface is touched with the body part and, when the body part is moved across the sensor surface in contacting fashion, outputs relative coordinates representing the amount of movement. A touch panel is a device constructed by combining a display device such as a liquid crystal display with a touch pad. A fingerprint sensor is a device that acquires a fingerprint image by converting height variations on the finger skin surface, such as the ridges and valleys formed in the finger surface, into pixel values proportional to the distance between the sensor and the finger skin surface. There is also proposed a sensor that implements the function of a touch pad by using a fingerprint sensor.